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Interconnection Technologies

Interconnection Technologies. Routing III. Interdomain routing. Routing domains are independently funded Routing domains do not trust each other Routing domains may have different policies Static routing EGP - first interdomain routing protocol BGP - current path vector routing protocol.

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Interconnection Technologies

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  1. Interconnection Technologies • Routing III

  2. Interdomain routing • Routing domains are independently funded • Routing domains do not trust each other • Routing domains may have different policies • Static routing • EGP - first interdomain routing protocol • BGP - current path vector routing protocol

  3. Border gateway protocol (BGP) • Current version 4 standardized in RFC 1771 • Runs over TCP • Sequence of AS numbers comprises path • Select route based on preferences of path(s) • Can edit path in route advertisements • Can selectively advertise paths/routes • E-BGP versus I-BGP

  4. BGP attributes • Describe routes in BGP updates • Confusing descriptions • e.g. Well known attributes must be supported • e.g. Mandatory must be present in the update • Examples • AS path • Community • Unreachable

  5. Confederations • Group of ASs that appear as a single AS • A form of aggregation • May simplify routing policies • e.g. Don't go through confederation X rather than specifying each AS in the confederation • Sub-optimal routing may result • Multiple ASs in a path vector appear as a loop

  6. Message types • Open • First message when neighbors come up • Update • Contains routing information • Notification • Final message just before link is disconnected • Keepalive • Reassures reachability in absence of updates

  7. Route dampening • Routes that oscillate ripple through Internet • Consumes CPU and causes instability • Unstable (flapping) routes are penalized • For some period of time route is surpressed • Supression time can increase to a maximum • Supression of routes results in lost connectivity • Bigger/important netblocks dampen slowly

  8. Sample Cisco BGP configuration Router bgp 12345 bgp log-neighbor-changes network 128.160.0.0 mask 255.255.0.0 neighbor 36.5.1.1 remote-as 54321 neighbor 36.5.1.1 description E-BGP peer with XYZ corp. neighbor 36.5.1.1 password as54321password neighbor 36.5.1.1 version 4 neighbor 36.5.1.1 prefix-list invalid in neighbor 36.5.1.1 prefix-list announce out ip prefix-list invalid seq 10 deny 0.0.0.0/8 le 32 ip prefix-list invalid seq 20 deny 10.0.0.0/8 le 32 ip prefix-list invalid seq 30 deny 127.0.0.0/8 le 32 ... ip prefix-list announce seq 10 permit 128.160.0.0/16 ip prefix-list announce seq 20 deny 0.0.0.0/0 le 32

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